For example, Japanese Patent Application Publication No. 2008-84742 (JP 2008-84742 A) discloses providing a spider's web-like film of polyvinylidene fluoride (PVDF) on the surface of an electrode mixture layer. According to this publication, such a spider's web-like film of PVDF keeps electrode debris from forming and getting into the battery interior, enabling lithium ion secondary batteries having a low level of defectiveness and improved reliability to be obtained.
That is, according to the disclosure made in this publication, when there is no PVDF film formed on the surface of the electrode mixture layer, electrode powder adheres to the tacky side of tape that has been attached to the surface of the electrode mixture layer. However, when there is a PVDF film formed on the surface of the electrode mixture layer, electrode powder does not adhere to tape that has been attached to the electrode mixture layer surface. Hence, this publication discloses that the electrode does not readily fall off, suppressing the generation of electrode debris.